Cellular signal transduction is a fundamental mechanism whereby extracellular stimuli are relayed to the interior of cells and subsequently regulate diverse cellular, processes. These signals regulate a wide variety of physical responses in the cell including proliferation, differentiation, apoptosis and motility. The extracellular signals take the form of a diverse variety of soluble factors including growth factors as well as paracrine, autocrine and endocrine factors. By binding to specific transmembrane receptors, growth factor ligands communicate extracellular signals to the intracellular signalling pathways, thereby causing the individual cell to respond to extracellular signals. Many of these signal transduction processes utilize the reversible process of the phosphorylation of proteins involving specific protein kinases and phosphatases.
Protein kinases (PKs) play a critical role in the signal transduction process. It transfers the gamma phosphate group from ATP to specific amino acid residue in a functional protein, resulting in a series of biological responses. Protein kinases are classified into two groups, according to amino acid specificity as substrate in the process of the phosphorylation: serine/threonine kinases (STKs) and protein tyrosine kinases (PTKs).
The mechanism of tyrosine phosphorylation widely exists in the signal transduction process, and controls several cell functions such as mitosis, cell cycle progression and differentiation, etc.(Hanks and Hunter, 1995, FASEB J. 9:576-596; Cadena and Gill, 1992, FASEB J. 6:2332-2337; Schlessinger and Ullrich, 1992, Neuron 9:383-391; Vandergeer et al., 1994, Arum. Rev. Cell Biol. 10:251-337). Mutation, uncontrolled or abnormally high level expression of the protein tyrosine kinases have been shown to lead to the conversion of normal cell to neoplastic phenotype(Chiao et al., 1994, Cancer Metast. Rev. 9:63-80; Hunter, 1991, Cell 64:249-270).
Vascular endothelial growth factor (VEGF) was identified as aspecific growth factor acting on vascular endothelial cell, and has been found to have various functions such as stimulating proliferation of endothelial cells, increasing microvascular permeability and inducing angiogenesis (Hanks and Hunter, 1995, FASEB J. 9:576-596). VEGF is known to be the most effective and directly acting angiogenic protein. It is a diffusible endothelial cell-specific mitogen and vascular growth factor (Ferrara N et al., EndocrRev, 1997, 18, 4-25; Tofimura T et al., Hum Pharthol, 1998, 29, 986-991). The VEGF family currently includes six known members: VEGF-A, VEGF-B, VEGF-C, VEGF-D, VEGF-E, and placental growth factor (PDF), which are all forms of dimeric glycoprotein. All VEGF family members contain characteristic regularly spaced eight-cysteine residues referred to as the “cysteine knot” motif. Li ling et al. (Li ling et al., Acta Biochimica et Biophysica Sinica, 2002, 34(1), 21-27) revealed high VEGF expression in malignant tumor cells as well as the high expression of Flk-1, which implicates the existence of both autocrine and paracrine VEGF loops within the tumor. VEGF expression is clearly correlated with intra-tumoral microvessel density, and the VEGF concentration in tissues is correlated with prognosis of solid tumor such as breast cancer, lung cancer, prostate cancer and colon cancer. It is known that hypoxia plays a critical role in stimulating VEGF expression. In addition to the enhancement of gene transcription rate, hypoxia inducing VEGF gene expression in the tumour cell also promotes the stabilization of VEGF mRNA. Three different members that belong to the VEGFR family have been identified: VEGFR-1/Flt-1, VEGFR-2/Flk-1/KDR, and VEGFR-4/Flt-4. VEGFR-1 and VEGFR-2 belong to cell surface tyrosine kinase receptors whose expression is mainly restricted to tumor vascular endothelial cells. Vascular endothelium growth factor (VEGF) and vascular endothelial growth factor receptor (VEGFR) play an important role in the process of tumor angiogenesis and has been validated as an important target for anti-cancer biotherapy.
Five strategies targeting the VEGF and VEGFR for anti-tumor therapy will be discussed as follows: 1. Gene therapy (Ellis L M et al. J Biol Chem 1998, 273, 1052-1057): VEGF and VEGFR have been implicated in positive regulation of the tumor angiogenesis. Gene therapy reduces VEGFNEGFR expression or disrupts the signal transduction pathways to inhibit their biological activities. 2. Anti-VEGFNEGFR monoclonal antibodies (Gordon M et al. Proc Am Soc Clin Oneol, 1998, 17, 2IIa): monoclonal antibodies against VEGFNEGFR block the secreted VEGF and VEGFR, and disrupt intracellular VEGF signal transduction to inhibit angiogenesis. 3. Small-molecule inhibitors: the series of su compounds developed by Sugen. 4. Soluble VEGFR: it binds with VEGF, but has no function of signal transduction. 5. Directed therapy: the two main VEGF receptors of Flt-1 and Flk-1/KDR overexpress in tumor vascular endothelial cell, but cannot be dected in adjoining normal tissue vascular endothelium. Hence, VEGF and VEGFR provide the specific target for tumor-directed therapy. VEGF can be combined with other anti-tumor agents, toxins, radionuclides for tumor-directed therapy.
Based on the tyrosine kinase inhibitor SU-14813 and the effective anticancer agent of pyrrolofused six-membered aza-heterocyclic derivatives A, the present invention is directed to design the analogues of formula (I). The compounds of the invention have obvious structure differences with the existing compounds in prior art, and they also show more efficiency and more function.
